How do radio telescopes track asteroids? I don't imagine that asteroids would be emitting radio waves, and their small size wouldn't seem to be an advantage either (though, a few miles across might be plenty to interrupt/reflect radio wavelengths? I dunno)
Just like with radar, it's an active process. The telescope emits radio waves, they are reflected by the object, and the telescope receives the reflected waves.
With clever tricks they can then get a hint of the size or other parameters of the object from the shape of the reflected signal.
> Relying upon high-powered terrestrial radars (of up to one MW[3]), radar astronomy is able to provide extremely accurate astrometric information on the structure, composition and movement of Solar System objects.[4] This aids in forming long-term predictions of asteroid-Earth impacts, as illustrated by the object 99942 Apophis. In particular, optical observations measure where an object appears in the sky, but cannot measure the distance with great accuracy (relying on parallax becomes more difficult when objects are small or poorly illuminated). Radar, on the other hand, directly measures the distance to the object (and how fast it is changing). The combination of optical and radar observations normally allows the prediction of orbits at least decades, and sometimes centuries, into the future.
Indeed, the fact that Mercury is not tidally-locked with the Sun was discovered using the Arecibo radar telescope. If I remember correctly, they used the Doppler shift imparted to the radio wave --which expresses differently across the width of the rotating planet -- to learn this.
"The rotation of Mercury was not discovered until 1965. Until then the most widely accepted theory had Mercury tidal locked to the Sun. Soviet scientists bounced radar signals off the planet’s surface in 1962 verifying that the planet rotated, but it wasn’t until scientists using the Arecibo Observatory verified the planet’s sidereal rotational period of 58.647 day."
I had to look this up on Wikipedia[1], it can apparently transmit as well as listen the way that most radio telescopes do and in at up to 20 TW too. I had frankly thought the most powerful radars in the world were in the 10s of MW range and this thing has got a dish 305m in diameter compared to the 10-50m I'm used to for radars tracking satellites in orbit (I used to do software for that professionally).
I wouldn't have thought doing active radar scans of an astroid out in space was possible given that radar returns fall off as the 4th power of range. But given that power and dish size, given that these are large objects being tracked, and given that they move slowly compared to the radar cone I guess it's possible after all. But then again one of the first ballistic missile defense radars accidentally mistook the rising Moon for an attack and almost caused WWIII[2] so I guess there's precedent, even though the Moon is much larger and closer. I'm seeing references to it tracking asteroids in the Apollo group, so relatively nearby[3] and plates which are much larger. I'd guess that even the biggest asteroid in the main belt, 1 Ceres, would be too dim for it to see but I'm curious.
> But then again one of the first ballistic missile defense radars accidentally mistook the rising Moon for an attack...
They are in good company; like 90% of UFO sightings are just people seeing the Moon and mistaking it for something else (or rather, not immediately identifying it, leaving them with impressions like "there was a bright light following me down the road" or "there was a glowing orb behind the trees").
Regarding the 20TW from the Wikipedia page, that's referring to the EIRP - effective isotropic radiated power. This is the amount of power that you would need to radiate from a theoretical antenna with a perfectly spherically symmetric power distribution. The Arecibo antenna has a fairly narrow beam. The 20TW EIRP transmitter appears to operate at 2.38GHz. Plugging that frequency and the 270m diameter, a beamwidth calculator gives me a gain of about 75dBi. So, yes, it's like a 20TW transmitter, but only one tiny narrow little slice of it. At 75dBi gain, that's one (10^7.5)th of the total sphere, about 1 part in 30 million. Or, you could say, if the antenna were radiating the same power in every direction as it does in it's peak direction, that would be 30 million times as much power. So, dividing to find the power in that narrow beam, we get "only" about 600kW radiated in the direction it is pointing. Add in cable losses and other inefficiencies, and the power output at the amplifier is probably close to a megawatt.
I used to work for NRAO. Arecibo is a transmitter, which illuminates the asteroid with very high powered radio waves. The asteroid reflects some of the radio waves, which is received back on the ground at Arecibo or at other radio telescopes like Greenbank or the Very Large Array.
Before Trump made my home island famous, Arecibo Observatory was the one place I could point to mainland American friends so they recognized Puerto Rico (since it's famous, used in scifi movies, etc.)
Hope the government assists in reconstructing the dish.
This can happen on sites where you have an adblocker removing modal overlays elements but there are still an invisible part or other CSS means limiting scrolling.
> Also, the pictures in that article made me feel nostalgic playing Golden Eye on the N64.
Recently a mate and I plugged in an n64 to play Golden Eye and spent way too long messing with the cables before realising that it was displaying correctly and that the graphics just weren’t that great.
A 15 inch CRT hid a lot too.
We still had a great time - no Oddjob usage per house rules. Using him is cheating.
No - Goldeneye 25 was a completely different project, focusing on singleplayer. Just a couple of days ago it had a takedown notice and its twitter feed is now gone:
They are now Spies Don't Die, and are making it a 90s-themed shooter that will be reminiscent of, but not a remake of, Goldeneye: https://twitter.com/spiesdontdie
Unfortunately, everything surrounding this remake implies that the project is dead and gone. The Twitter account and the IndieDB entry have both been deleted.
YOu have to allow JS to view the images and load the actual text of the article too! How did we get to this stage where you can't even just view a images and text without JS.
Because the people who put ads and paywalls on their sites are in an active war against adblockers and dynamically loading all the content is an effective countermeasure for not allowing JavaScript?
Seems like such a strange break. I feel like there's supposed to be a dramatic piece of video in slow-mo showing one strand breaking, then the additional stress causing the next one to snap, until the final 'plink' before the whole thing comes crashing down.
Interesting to me that everyone is calling this a "cable".
It might be the combination of climbing/sailing/rigging/nerd ... but I'd never call that structural element that broke a cable.
The only cables I can think of either carry electrons, photons, or signal wires (say, a clutch cable). I'm being maybe pedantic, curious what others think, esp in industry.
66 comments
[ 3.5 ms ] story [ 111 ms ] threadWith clever tricks they can then get a hint of the size or other parameters of the object from the shape of the reflected signal.
https://en.wikipedia.org/wiki/Radar_astronomy
"The rotation of Mercury was not discovered until 1965. Until then the most widely accepted theory had Mercury tidal locked to the Sun. Soviet scientists bounced radar signals off the planet’s surface in 1962 verifying that the planet rotated, but it wasn’t until scientists using the Arecibo Observatory verified the planet’s sidereal rotational period of 58.647 day."
(From: https://www.universetoday.com/14008/rotation-of-mercury/)
I wouldn't have thought doing active radar scans of an astroid out in space was possible given that radar returns fall off as the 4th power of range. But given that power and dish size, given that these are large objects being tracked, and given that they move slowly compared to the radar cone I guess it's possible after all. But then again one of the first ballistic missile defense radars accidentally mistook the rising Moon for an attack and almost caused WWIII[2] so I guess there's precedent, even though the Moon is much larger and closer. I'm seeing references to it tracking asteroids in the Apollo group, so relatively nearby[3] and plates which are much larger. I'd guess that even the biggest asteroid in the main belt, 1 Ceres, would be too dim for it to see but I'm curious.
[1]https://en.wikipedia.org/wiki/Arecibo_Observatory
[2]https://blog.ucsusa.org/david-wright/the-moon-and-nuclear-wa...
[3]https://en.wikipedia.org/wiki/Apollo_asteroid
They are in good company; like 90% of UFO sightings are just people seeing the Moon and mistaking it for something else (or rather, not immediately identifying it, leaving them with impressions like "there was a bright light following me down the road" or "there was a glowing orb behind the trees").
Before Trump made my home island famous, Arecibo Observatory was the one place I could point to mainland American friends so they recognized Puerto Rico (since it's famous, used in scifi movies, etc.)
Hope the government assists in reconstructing the dish.
There was an episode of Agents of S.H.I.E.L.D. set in San Juan, though. So now there's something else mainlanders have heard of.
It seems clear what happened here. Aliens.
Also, the pictures in that article made me feel nostalgic playing Golden Eye on the N64.
Recently a mate and I plugged in an n64 to play Golden Eye and spent way too long messing with the cables before realising that it was displaying correctly and that the graphics just weren’t that great. A 15 inch CRT hid a lot too.
We still had a great time - no Oddjob usage per house rules. Using him is cheating.
https://www.youtube.com/watch?v=R55y17rXdt4&feature=emb_titl...
https://geshl2.com
https://twitter.com/007GoldenEye25/status/129309061086227251... (the tweet announcing it)
They are now Spies Don't Die, and are making it a 90s-themed shooter that will be reminiscent of, but not a remake of, Goldeneye: https://twitter.com/spiesdontdie
Probably because you watched Goldeneye :). In that movie the dish looks like it's concrete:
https://www.youtube.com/watch?v=FtKJpr7N1qc
https://www.youtube.com/watch?v=wGmDAjRRNXs
https://www.youtube.com/watch?v=jp9tENRDVzA
https://oyster.ignimgs.com/mediawiki/apis.ign.com/frontlines...
https://oyster.ignimgs.com/mediawiki/apis.ign.com/frontlines...
Source: https://www.ign.com/wikis/frontlines-fuel-of-war/Mutliplayer...
Thanks to article on sciencealert.com: https://www.sciencealert.com/a-broken-cable-smashed-a-huge-h...
Looks like that applies here, as well...
It might be the combination of climbing/sailing/rigging/nerd ... but I'd never call that structural element that broke a cable.
The only cables I can think of either carry electrons, photons, or signal wires (say, a clutch cable). I'm being maybe pedantic, curious what others think, esp in industry.
On a suspension bridge, what are the catenary pieces called?
Last time I checked nautical cables do not carry photons or signals. Arresting cables, bowden cables are also cables that do not do so.
I'd argue that a Bowden cable (eg a clutch cable) is primarily carrying a signal... really though, just thinking through what defines a cable.
By contrast, rope and line are terms with fairly specific meanings.